List of comets with no meaningful orbit
This is a list of comets designated with X/ prefix. The majority of these comets were discovered before the invention of the telescope in 1610, and as such there was nobody to plot the positions of the comets to a high enough precision to generate any meaningful orbit. Later comets, observed in the 17th century or later, either did not have enough observations, sometimes as few as one or two, or the comet disintegrated or moved out of a favorable location in the sky before it was possible to make more observations of it.
| Comet | Discoverer |
| X/-233 B1 | |
| X/-156 U1 | |
| X/-137 K1 | |
| X/-134 N1 | |
| X/-119 K1 | |
| X/54 L1 | |
| X/60 P1 | |
| X/79 F1 | |
| X/422 F1 | |
| X/595 A1 | |
| X/607 U1 | |
| X/626 F1 | |
| X/676 P1 | |
| X/838 V1 | |
| X/839 B1 | |
| X/841 Y1 | |
| X/864 H1 | |
| X/875 L1 | |
| X/891 J1 | |
| X/941 R1 | |
| X/975 P1 | |
| X/998 D1 | |
| X/1033 E1 | |
| X/1034 S1 | |
| X/1056 R1 | |
| X/1106 C1 | |
| X/1338 G1 | |
| X/1381 V1 | |
| X/1391 J1 | |
| X/1432 C1 | |
| X/1491 B1 | |
| X/1529 P1 | |
| X/1569 V1 | |
| X/1577 U1 | |
| X/1621 B1 | |
| X/1702 D1 | |
| X/1846 U1 | Hind |
| X/1872 X1 | Pogson |
| X/1951 G1 | |
| X/1951 G2 | |
| X/1951 K1 | |
| X/1952 C1 | Weinberger |
| X/1954 C2 | Weinberger & Auner / Palomar DSS |
| X/1954 V1 | Hartl |
| X/1954 V2 | Meyer/Palomar DSS |
| X/1955 G2 | Auner & Dengel & Weinberger / Palomar DSS |
| X/1975 J1 | Eberst |
| X/1975 T3 | West |
| X/1976 U2 | Eberst & Coulson & Tritton |
| X/1978 W1 | West & Schuster |
| X/1979 O2 | Kowal |
| X/1979 O3 | Kowal |
| X/1987 A2 | McNaught & Hartley |